Camber change after 1.5" drop?

[JMortensen]

IME adding caster probably added more front grip than just about anything else I did, and my Z understeered badly before I upped the caster. I pushed it up to about 5 degrees and it really made a nice difference. STB also made a huge difference. I like toe out for the front end too, but mine isn't a daily. When it was I had 2 marks on one tie rod, and I used to bring slicks with me and I'd move the tie rod from one mark to the other while switching tires. Different drivers like different setups I guess. Lots of autoxers running more than 3 degrees of caster.

[Chickenman]

Yes, there is definitely more than one way to skin a cat.  I don't like car with really heavy steering. I prefer steering that is reasonably light so I can initiate quick corrections.  I can't drive a non-Power Steering car with 5 degrees of Camber the way I like.  I tend to drive more with my wrists than my arms. I don't use a lot of steering turn angle. Plus I don't have big arm Muscles...

 

I like a car that is very much " On the nose " and a little " Loose ".  .Fellow Autocrossers have driven my cars and most don't " initially " like how twitchy my cars are. Once they get some seat time tough, it gets a lot more comfortable and quicker.

 

It makes for very quick turning car and one that excels in lineal slaloms and tight corners. Car is on a knife edge though and you have to be very precise on fast sweepers. And most important... it works for me and brings home the Trophies

 

Strange thing is, I've never had to resort to Toe-Out, or a large amount of Castor or Camber to get the Nose to turn on hard and take a set...on any of my Race cars. But I also run a LOT of rear brake Bias ( that really helps rotate the car ), Trail Brake and I will often run rubber frame bushings on the front bar. Depending on the thickness of the bushing, this will reduce the initial stiffness of the front bar by 10 to 20% on initial turn-in ( Compared to Poly bushings ), but as it compresses the rubber stiffens. Give a type of progressive front bar rate, so the car turns in quickly initially , then once the front end has taken a set, stiffens up to prevent roll. IME this has worked well over the years.... for me.

 

I also use a smaller bar for the front when Autocrossing than when I am Road Racing or Hillclimbing. EG: On my heavily Modified Camaro, I would run a 32 mm hollow Front bar with Rubber frame bushings ( They aren't very thick ). At Hillclimbs or Track Days I would run a 34mm hollow Front bar with Poly frame bushings. Both bars were adjustable. For the higher speed events a tad of under-steer is nice. Just a tad though for me... I hate under-steer.

 

One thing I do highly believe in is fine tuning  car rotation with rear brake bias. Probably comes from my Rally Car days, but it is very effective... especially in Autocross.

 

The most important thing is to get a setup that you are comfortable with.... and is fast of course.  That takes seat time and test days. Fortunately our local scene has lots of both.

Edited July 20, 2016 by Chickenman

[RebekahsZ]

The stock Z car toes-out under braking.

Edited July 22, 2016 by RebekahsZ

[Chickenman]

 

The stock Z car toes-out under braking.

 

 

Hmm... this could be an interesting Technical discsussion

 

Interesting because the Z is a front steer ( Steering arms ahead of axle centerline ). Front steer cars normally have neutral or Toe-in under braking. Thrust forces under braking, push control arm rearwards as suspension bushing compressed. Steering Tie Rods are shortened in Arc, which pulls steering arms closer to each other . This adds Toe-in under braking to counter-act the natural Drag forces on the tire that is trying to add Toe out.

 

Rear steer cars ( Steering arms behind axle center--line ) can be a bit more problematic. Deflection changes in the control arm tend to add Toe-Out unders braking ( and cornering )

 

There are a few examples of this type of discussion on FSAE forums, but Herb Adams mentioned some of the advantages of Front Steer in his book " Chassis Engineering " on page 58. Interesting reading:

 

https://books.google.ca/books?id=rY2ujnNrhf0C&pg=PA58&lpg=PA58&dq=Effect+of+Front+steer+and+rear+steer&source=bl&ots=HgODf6wQ6C&sig=VD1jWdUzvn0i9OrrvmtN7ww1XXs&hl=en&sa=X&ved=0ahUKEwihk5mNwYfOAhVV92MKHXwGDFQQ6AEIJzAB#v=onepage&q=Effect%20of%20Front%20steer%20and%20rear%20steer&f=false

[Chickenman]

I think I'm going to drag my copy of Herb's book off the book shelf and read through it again. I've forgotten just how excellent that book is...

[JMortensen]

It toes out under compression, which happens under braking. Stock TC and LCA bushings might allow more toe change than the bumpsteer creates, but who is running stock bushings???

[RebekahsZ]

I'm just stating facts as I observe them physically-I don't yet understand the "why" of it. Over the next month or two, I'm gonna be trying to adjust this tendency out if I can. When I autocross (really not more than a couple times a year) or a track day (once a year), I let other folks drive my car, sometimes with me in the car, sometimes I just let other folks take it. I get lots of compliments on how well it turns in (it's the only car I've ever driven hard), and I get suggestions on how to improve the car and my driving. Since the car toes-out on forward weight transfer, I don't think we need to run a lot of static toe. Just fly up to the corner and pile on the brakes, then turn before the front unloads. If you don't slow enough, you won't have enough traction to change directions-go too slow and you lose time and exit speed. Getting that little maneuver together is pretty hard in and of itself. But it's not the car so much as the driver. I DO think I'm running too much camber and it is hurting my straight line braking. I'd like to come from -3.5 to -2.5 but my bolt in camber plates limit precise adjustment.

[NewZed]

Ignoring bumpsteer (I think I know what that means) you can see that the flexible components of the front suspension can lead to toe-out as the wheels get pushed back.  The steering gear can remain static, while the bushings compress.  Braking must put some extra strain/wear on the steering gear also since it ends up under a higher tensile load.  Urethane or solid bushings at the T/C rod and control arm probably help it last longer, and reduce toe-out.

 

 

[JMortensen]

Urethane at the TC rod tends to break the TC rods. A solid heims joint or inner tie rod end allows free movement without squishiness.

 

Old thread with multiple broken TC rods:

http://forums.hybridz.org/topic/22762-scary-tension-rod-failure/

[NewZed]

I thought that was a given.  Urethane in front, rubber in back.

[mtnickel]

So since I couldn't find it,

Here is how much camber was on a stock 260z (that's been hit in a couple places). This was about a 2" drop, or a 2 finger tire gap on 205/55r16

 

Rear 1.5* of camber

Front 0, +.2*

By slotting the fronts I was only able to get about .3-.4 negative camber. The stock isolator bottoms out in the tower. So if you're going to slot there, you can only get about .4-.5* in the negative direction. The rears I slotted both ways (probably didn't need to slot so far in the negative direction). I dialled it back to about 1.25* negative.

 

Fronts will need adjustable lower arms. The slotted stock uppers could still be useful as with the positive and negative range I'll have about 1* total to play with. Can then set the lower to a give most of change and upper to fine tune. Maybe move between street and autocross setup.

Edited July 28, 2016 by mtnickel

[Chickenman]

You can get Camber plates that replace the Top isolator mount. No major cutting or welding of strut towers required. I have a set of these ready to install this winter. You can make these work with stock springs or 2.5" Coil overs. They also gain you some shock travel.

 

http://www.ebay.com/itm/MK1-PillowBall-Bearing-Strut-Upper-Mount-For-Coilover-Kit-Mounts-Plates-240Z-/161203739866?fits=Model%3A240Z&hash=item25887ddcda:g:CwUAAOxygPtS3Kbw&vxp=mtr

 

Edited July 29, 2016 by Chickenman

[74_5.0L_Z]

One option that hasn't been discussed is the JTR mod to the front crossmember. The JTR mod relocates the attach point for the lower control arm up 3/4" and outboard 1/4" (going by memory). This will yield some negative camber and improve the camber gain on a lowered car.

[Chickenman]

One option that hasn't been discussed is the JTR mod to the front crossmember. The JTR mod relocates the attach point for the lower control arm up 3/4" and outboard 1/4" (going by memory). This will yield some negative camber and improve the camber gain on a lowered car.

 

Yeah, I did that to my Race 510's and 1200's. Works very well.  Doesn't matter on a Street car , but  some Autocross and Race classes don't allow modifying of stock suspension mounting points

[RebekahsZ]

Nobody checks til you start winning.

[Chickenman]

Nobody checks til you start winning.

 

Truer words were never spoken.. LOL

[74_5.0L_Z]

If you run EMOD then rules are not a problem. Any suspension, any brakes, any engine just as long as you are not less than 1750 lbs.

[mtnickel]

I'm glad this thread could be such a catalyst for suspension discussion!

 

So I'll likely go the way of an adjustable lower arm. May relocate the inner pivot while I'm at it to get a little more arm angle. Don't really want to mess with the engine though, so if it looks like too much trouble to do on the car, i'll leave it for now.

 

Regarding adjustable arms,

Where did everyone settle on what quality of Rod end to get. I'll likely go 3/4" and then get reducer bushings. The purist in me wants to just make the bushings custom for the 14mm bolt instead of 5/8". Something about putting an imperial fastener on a Jap car just ERks me.

Important to get chromoly, teflon lined, etc? or would an economy rod do since I'm already up to the 3/4" size. Aurora 3/4" CW are like 14,000 lb static load I believe. 

 

As a final note, It's be an absolute blast to get the Z on the road. I had it on the road for just a couple weeks last year for the first time before I blew a rear hardline brake line. 

Now I'm dailying it for the summer and loving it. Upgraded to vented fronts w/S12W's. Contrary to JohnM, I feel I have enough balance with the 43mm early 280zx rears. The Piston area calculations all seemed to work out and on my first brake check with full rear bias, the rear stepped out first. 

 

I must say, the 175/200 spring rates seem MORE than stiff enough for a street/AutoX ride. It's one of the stiffest I've been in, but the level handling (with next to no sway bars) and cornering is sure worth the occational rough road and chassis squeaks.

 

I'll be updating my RB25 thread shortly with all my fun brake pics, sectioning, LSD swap, etc.

 

Thanks guys for the fun discussion and community.

Edited July 30, 2016 by mtnickel

[Chickenman]

Aurora is hard to beat for quality and longevity. Get the best you can for the control arm Heims as they get a lot of constant movement. For a DD, I would get Teflon lined and use seals. For a Panhard rod, you don't really need Teflon lined because thye don't get the movement that A-Arms do.

 

One thing that will extend the life of your Heim joints are dirt seals . There are two types. A saucer shaped type and a full boot type. You can order them online ( Summit, Jegs etc )  or get them at most 4x4 Performance shops. I think Mopac carries them locally. " Seals-It is a popular brand. .

 

http://www.speedwaymotors.com/Seals-It-WS3125-Heim-Joint-Rod-End-Seals-5-16-Inch-Hole-Set-6,1528.html

 

 

[Chickenman]

Edit: Another product that is readily available now, is bump steer spacers. These correct the geometry of the A-Arm on lowered cars so it has a downwards slope again ( important for Camber gain during cornering, particularly on Mac struts ) and they also reduce Bump steer.

 

It's a bit more elegant solution than moving the pivot location upwards. Relocating the pivot upwards corrects the Camber curve in roll, but does nothing to correct Bump steer. Something to consider.

 

You can get software programs to analyze suspension movement. Price varies all over the map and depends on complexity. A little searching on Google will even find some Free programs. Usually Trial periods with limitations on function, but there are some Fully functional " Freeware" or Shareware programs that are fully functional. I personally haven't tried them though. 

 

Formula SAE sites are usually good. Student rates are also available. Here is one Free version that may be useful:

 

http://suspensioncalculator.com/download.html

 

There are also some basic " Real Time " models/calculators that you don't even have to download. This looks promising: Note: Logging in unlocks some more functions.

 

http://www.racingaspirations.com/

 

And the Mac Strut calculator:

 

http://www.racingaspirations.com/apps/macpherson-geometry-calculator

Edited August 1, 2016 by Chickenman